The major part of disturbs in electrical systems occurs in transmission lines. These disturbs are in most cases single-phase and transitory and mainly caused by atmospheric electrical discharges. In this paper, the voltage-current cross relation characteristic of the secondary arc was investigated using open air experimental data. With more than 500 artificially generated long electrical arcs, a methodology to calculate the stationary secondary arc conductance and capacitance is presented, alongside with the capacitive and conductive values for several arc currents, which were varied from 15 A rms to 500 A rms .